Single-layer type electrophotosensitive material and image forming apparatus using the same

ABSTRACT

The present invention provides a single-layer type electrophotosensitive material comprising a conductive substrate and a photosensitive layer formed on the conductive substrate, wherein the photosensitive layer contains a phthalocyanine compound as an electric charge generating material, a hole transferring material and an electron transferring material in a binder resin, and that a difference in absolute value between a plus polarity sensitivity and a minus polarity sensitivity measured under the conditions of an exposure wavelength of 780 nm and an exposure energy of 1.0 μJ/cm 2  is not more than 500  312 V, and a reversal development type digital image forming apparatus using the electrophotosensitive material, which does not include a charge neutralizing step.

This application claims priority to Japanese Patent Application No.1999-302914, filed on Oct. 25, 1999, the disclosure of which isincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a single-layer typeelectrophotosensitive material which is used in digital image formingapparatuses such as electrophotosensitive copying machine, facsimile andlaser beam printer, and a digital image forming method using the same.

More particularly, the present invention relates to a single-layer typeelectrophotosensitive material, which does not generate a memory imageeven when using in a reversal development type digital image formingapparatus including no charge neutralizing step, and a reversaldevelopment type digital image forming method using the same, which doesnot include a charge neutralizing step.

Recently, an organic photosensitive material has widely been usedbecause of its easy production, low cost, wide range of choice ofphotosensitive materials such as electric charge transferring material,electric charge generating material and binder resin, and highfunctional design freedom as compared with a conventional inorganicphotosensitive material.

The organic photosensitive material includes, for example, single-layertype photosensitive material wherein an electric charge transferringmaterial (hole transferring material, electron transferring material) isdispersed in the same photosensitive layer, together with an electriccharge generating material, and multi-layer type photosensitive materialcomprising an electric charge generating layer containing an electriccharge generating material and an electric charge transferring layercontaining an electric charge transferring material, which are mutuallylaminated. The single-layer type photosensitive material has attractedspecial interest recently because it has such an advantage that opticalcharacteristics can be improved due to simple layer structure, excellentproductivity and less interfaces between layers.

On the other hand, an image forming apparatus using anelectrophotosensitive system is capable of charging a photosensitivematerial (principal charge step), exposing an image to form a staticlatent image (exposure step), developing the static latent image with atoner at a state where a developing bias voltage is applied (developmentstep) transferring the formed toner image to a transfer paper (transferstep), and fixing to form an image. The residual toner on thephotosensitive material is cleaned by a urethane blade (cleaning step)and the residual electric charges on the photosensitive material areneutralized by LED (charge neutralizing step).

To reduce the size of the image forming apparatus and initial cost,various trials of omitting the cleaning step and charge neutralizingstep have been made.

The image forming apparatus using an electrophotosensitive systemincludes, for example, digital and analogue copying machines, facsimileand laser beam printer. In particular, a reversal development system fordeveloping using a toner having the same polarity as that of a chargingvoltage to be applied to the photosensitive material in the charge stephas widely been used in a digital image forming apparatus.

However, the following problems such as generation of a memory imageoccur when using a conventional electrophotosensitive material in areversal development type digital image forming apparatus.

<Transfer memory>

When using an electrophotosensitive material in a reversal developmenttype digital image forming apparatus, a transfer voltage to be appliedto the electrophotosensitive material in a transfer step is usuallyapplied through a transfer medium (paper) without being applied directlyto the electrophotosensitive material, and the transfer voltage is notapplied when the transfer medium does not pass through the transferstep.

However, on-off timing of the transfer voltage is very difficult andportion to be applied directly to the photosensitive material is oftengenerated with respect to front/rear portions of the transfer medium.That is, application of the transfer voltage starts before atransferring apparatus is covered with the front portion of the transfermedium. Furthermore, the transfer voltage is continuously applied evenif portion of the transferring apparatus is exposed by passage of therear end of the transfer medium so that the transfer voltage is applieddirectly to the photosensitive material at said portion.

In case of a positively charging single-layer type photosensitivematerial, since the polarity of the voltage to be applied in thetransferring apparatus is negative, negative space electric charges areremained at the portion of the photosensitive material to which anegative voltage has been applied. Generally, a single-layer typephotosensitive material has sensitivity in both polarities so thatnegative space electric charges are neutralized in the following chargeneutralizing step.

However, in case where the sensitivity of the positively chargingsingle-layer type photosensitive material to the negative polarity isdrastically inferior (mobility of the electron transferring material isvery small) or the photosensitive material is used in the image formingapparatus including no charge neutralizing step, negative space electriccharges are not sufficiently neutralized and a reduction in potential iscaused by an influence of space electric charges even if thephotosensitive material is positively charged in the following chargestep. Furthermore, a difference in sensitivity appears in thedevelopment step, thus causing such problems that said portion turnsinto black in the image (memory image).

<Exposure memory>

After passing through the exposure step and development step, positiveelectric charges on the surface of the positively charging single-layertype photosensitive material are uniformly neutralized in the chargeneutralizing step usually, and the photosensitive material is positivelycharged uniformly in the following charge step.

Similar to the case of the transfer memory, the negative space electriccharge density of the exposed portion is larger than that of thenon-exposed portion and a difference in potential appears in thefollowing charge step and the memory image is liable to be generated incase where the sensitivity of the positively charging single-layer typephotosensitive material to the negative polarity is inferior and thephotosensitive layer is used in the image forming apparatus including nocharge neutralizing step.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide a single-layertype electrophotosensitive material, which hardly generates a exposurememory and a transfer memory and does not generate a memory image evenwhen using in a reversal development type image forming apparatusincluding no charge neutralizing step.

Another object of the present invention is to provide a reversaldevelopment typedigital image forming apparatus using the single-layertype electrophotosensitive material, which does not include a chargeneutralizing step.

The present inventors have intensively studied to attain the aboveobjects and found the fact that a single-layer typeelectrophotosensitive material comprising a conductive substrate and aphotosensitive layer formed on the conductive substrate, characterizedin that the photosensitive layer contains a phthalocyanine compound asan electric charge generating material, a hole transferring material andan electron transferring material in a binder resin, and that adifference in absolute value between a plus polarity sensitivity and aminus polarity sensitivity measured under the conditions of an exposurewavelength of 780 nm and an exposure energy of 1.0 μJ/cm² is not morethan 500 312 V hardly generates an exposure memory and a transfer memoryand does not generate a memory image even when using in a reversaldevelopment type image forming apparatus including no chargeneutralizing step. They have further studied based on this finding, thuscompleting the present invention.

The present invention includes the following inventions:

-   -   (1) a single-layer type electrophotosensitive material        comprising a conductive substrate and a photosensitive layer        formed on the conductive substrate, wherein the photosensitive        layer contains a phthalocyanine compound as an electric charge        generating material, a hole transferring material and an        electron transferring material in a binder resin, and a        difference in absolute value between a plus polarity sensitivity        and a minus polarity sensitivity measured under the conditions        of an exposure wavelength of 780 nm and an exposure energy of        1.0 μJ/cm² is not more than 500 312 V;    -   (2) The single-layer type electrophotosensitive material        according to the term (1), wherein the absolute value of the        plus polarity sensitivity is smaller than that of the minus        polarity sensitivity;    -   (3) The single-layer type electrophotosensitive material        according to the term (2), which contains, as the hole        transferring material, a compound represented by the general        formula (1):    -    wherein R¹ and R³ are the same or different and each represents        an alkyl group which may have a substituent, an aryl group which        may have a substituent, or an aralkyl or alkoxy group which may        have a substituent; and R² and R⁴ are the same or different and        each represents a hydrogen atom or an alkyl or alkoxy group        which may have a substituent, provided that R² and R⁴ are        hydrogen atoms when R² and R⁴ are substituted at the        para-position;    -   (4) The single-layer type electrophotosensitive material        according to the term (2), which contains, as the electron        transferring material, at least one selected from the group of        compounds represented by the general formula (2):    -    wherein R⁵ represents a halogen atom, or an alkyl or aryl group        which may have a substituent; and R⁶ represents an alkyl or        alkoxy group which may have a substituent, or a group:        —O—R^(6a), which represents an alkyl or aryl group which may        have a substituent;    -   the general formula (3):    -    wherein R⁷ and R⁸ are the same or different and each represents        an alkyl group, a halogenated alkyl group, an aryl group, an        aralkyl group, an alkoxy group, an aryloxy group, an aralkyloxy        group, an acyl group, an alkoxycarbonyl group, an        aryloxycarbonyl group, an aralkyloxycarbonyl group, or a nitro        group; and n represents an integer of 0 to 3;    -   the general formula (4):    -    wherein R^(9a), R^(9b), R^(9c) and R^(9d) are the same or        different and each represents a hydrogen atom, or an alkyl or        aryl group which may have a substituent; and    -   the general formula (5):    -    wherein R¹⁰ and R¹¹ are the same or different and each        represents an alkyl group, a halogenated alkyl group, an aryl        group, an aralkyl group, an alkoxy group, an haryloxy group, an        aralkyloxy group, an acyl group, an alkoxycarbonyl group, an        aryloxycarbonyl group, an aralkyloxycarbonyl group, or a nitro        group, and n represents an integer of 0 to 3;    -   (5) The single-layer type electrophotosensitive material        according to the term (2), which contains, as the hole        transferring material, a compound represented by the general        formula (1) and, as the electron transferring material, a        compound represented by the general formula (2).    -   (6) The single-layer type electrophotosensitive material        according to the term (2), wherein the content of the        phthalocyanine compound is from 0.1 to 4.0% by weight based on        the weight of the binder resin;    -   (7) The single-layer type electrophotosensitive material        according to the term (2), which contains, as the binder resin,        a bisphenol Z type polycarbonate resin having a weight-average        molecular weight of 15,000 to 100,000;    -   (8) The single-layer type electrophotosensitive material        according to the term (2), wherein the film thickness of the        photosensitive layer is from 10 to 35 μm;    -   (9) A method of producing a single-layer type        electrophotosensitive material comprising a conductive substrate        and a photosensitive layer formed on the conductive substrate,        the photosensitive layer containing a phthalocyanine compound as        an electric charge generating material, a hole transferring        material and an electron transferring material in a binder        resin, wherein the photosensitive layer is formed by selecting        the phthalocyanine compound, hole transferring material,        electron transferring material and binder resin so that a        difference in absolute value between a plus polarity sensitivity        and a minus polarity sensitivity is not more than 500 312 V        under the measuring conditions of an exposure wavelength of 780        nm and an exposure energy of 1.0 μJ/cm².    -   (10) The method of producing a single-layer type        electrophotosensitive material according to the term (9),        wherein at least one selected from the group of the compounds        represented by the general formula (2), (3), (4) and (5) of the        term (4) is contained as the electron transferring material; and    -   (11) A reversal development type digital image forming apparatus        using the single-layer electrophotosensitive material of the        term (1), comprising at least a principal charge step, an        exposure step, a development step and a transfer step along the        forward direction of the electrophotosensitive material, wherein        a voltage to be applied in the transfer step has a polarity        reverse to a voltage to be applied in the charge step step,        which does not include a charge neutralizing step.

In the present invention, as described above, when using anelectrophotosensitive material wherein a difference in absolute valuebetween a plus polarity sensitivity and a minus polarity sensitivitymeasured under the conditions of an exposure wavelength of 780 nm and anexposure energy of 1.0 μJ/cm² is not more than 500 312V, an exposurememory and a transfer memory are drastically reduced. The reason isconsidered as follows. That is, the smaller a difference in absolutevalue of the sensitivity between a plus polarity and a minus polarity,the better the transferring balance between holes and electronsgenerated in the photosensitive layer. Thus, the memory is reduced.

As described above, the absolute value of the plus polarity sensitivityis smaller than that of the minus polarity sensitivity, that is, apositively charging type electrophotosensitive material is the mostcommon because design of an electron transferring material having largemobility is difficult and the mobility of the electron transferringmaterial is smaller than that of the hole transferring material and,furthermore, ozone is hardly generated in the image forming apparatus inthe above single-layer type electrophotosensitive material.

The single-layer type electrophotosensitive material according to thepresent invention preferably includes a positively charged type one asreferred to in the above terms (3) to (8).

In the present invention, the positively charging single-layer typeelectrophotosensitive material preferably contains the compoundrepresented by the general formula (1) as the hole transferring materialand at least one of the compounds represented by the general formulas(2), (3), (4) and (5) as the electron transferring material. The reasonis as follows. That is, by using the compound having high holetransferability or electron transferability, the sensitivity to thepositive or negative polarity is improved, which is very effective toreduce the memory.

As described in the term (6), even when using in a reversal developmenttype digital image forming apparatus including no charge neutralizingstep, the memory image is not generated because the single-layer typeelectrophotosensitive material of the present invention has a smallmemory.

As described above, even if the single-layer type electrophotosensitivematerial of the present invention is used in a reversal development typedigital image forming apparatus including no charge neutralizing step, amemory image is not generated because of very small exposure memory andtransfer memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship between a transfer memorypotential and an exposure memory potential, and a difference inabsolution value of sensitivity between a plus polarity and a minuspolarity of single-layer type electrophotosensitive materials ofExamples and Comparative Examples.

FIG. 2 is a diagram showing an original for evaluation of a transfermemory image, and a transfer memory image.

FIG. 3 is a diagram showing an original for evaluation of an exposurememory image, and an exposure memory image.

DISCLOSURE OF THE INVENTION

Various materials used in the single-layer type electrophotosensitivematerial of the present invention will be described in detailhereinafter.

Electric charge generating agent>

When using laser as a light source in a digital image forming apparatus,a semiconductor laser and LED are exclusively used in view of smallsize, cheap price and simplicity. Accordingly, an organic photosensitivematerial having sensitivity in a wavelength range from 700 to 850 nm isrequired. As the electric charge generating material which satisfies theabove requirement and used in the organic photosensitive material, forexample, polycyclic quinone compound, pyrylium compound, squaliumcompound, phthalocyanine compound and azo compound have been suggestedor put into practice. In the single-layer type electrophotosensitivematerial of the present invention, various phthalocyanine compounds areused.

In general, the phthalocyanine compound includes, for example,metal-free phthalocyanine (CGM-1) containing no center metal; titanylphthalocyanine (CGM-2) which has intensively been developed, recently;and metal phthalocyanine containing a center metal, such as aluminumphthalocyanine, vanadium phthalocyanine, cadmium phthalocyanine,antimony phthalocyanine, chromium phthalocyanine, copper4-phthalocyanine, germanium phthalocyanine, iron phthalocyanine,chloroaluminum phthalocyanine, chloroindium phthalocyanine,chlorogallium phthalocyanine, magnesium phthalocyanine, dialkylphthalocyanine, tetramethyl phthalocyanine, and tetraphenylphthalocyanine. The crystal form that can be used may be any of α, β, γ,δ, ε, σ, x and τ forms.

The phthalocyanine compound is preferably contained in the amount of 0.1to 4.0% by weight based on the weight of the binder resin. When thecontent of the phthalocyanine compound exceeds 4% by weight, a memorybecomes larger. The reason is as follows. That is, since carries areincorporated into a trap of the photosensitive layer to generateresidual carries as a memory, the number of residual carriers areincreased due to excess number of carrier. On the other hand, when thecontent is less than 0.1% by weight, it becomes difficult to put intopractice because of poor photosensitivity.

<Hole transferring material>

As the hole transferring material used in the single-layer typeelectrophotosensitive material of the present invention, a stilbenecompound represented by the general formula (1) can be used particularlypreferably. When using the stilbene compound as the hole transferringmaterial, the stilbene compound may be contained alone or at least oneof them may be contained. That is, various hole transferring materialsmay be contained, together with the stilbene compound.

Various hole transferring materials include nitrogen-containing cycliccompounds, for example, oxadiazole compound such as2,5-di(4-methylaminopheny))-1,3,4-oxadiazole, styryl compound such as9-4-(diethylaminostyryl)anthracene, carbazole compound such aspolyvinylcarbazole, organic polysilane compound, pyrazoline compoundsuch as 1-phenyl-3(p-dimethylaminophenyl)pyrazoline, hydazone compound,triphenylamine compound, indole compound, oxadiazole compound, isoxazolecompound, thiazole compound, thiadiazole compound, imidazole compound,pyrazole compound, and triazole compound.

The content of the hole transferring material is preferably from 5 to500% by weight, and more preferably from 25 to 200% by weight, based onthe weight of the binder resin.

<Electron transferring material>

As the electron transferring material used in the single-layer typeelectrophotosensitive material of the present invention, a quinonecompound represented by the general formula (2), (3), (4) or (5) can beused particularly preferably. When using the quinone compound as theelectron transferring material, the quinone compound may be containedalone or at least one of them may be contained. That is, other electrontransferring materials may be contained, together with the quinonecompound.

Other electron transferring materials include electron attractivesubstances, for example, pyrene compound, carbazole compound, hydrazonecompound, N,N-dialkylaniline compound, diphenylamine compound,triphenylamine compound, triphenylmethane compound, tetracyanoethyl,tetracyanoquinoedimethane, chloroanil, bromoanil,2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 52,4,7-trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone,and 2,4,8-trinitrothioxanthone, or those prepared by polymerizing theseelectron attractive substances.

The content of the electron transferring material is preferably from 5to 100% by weight, and more preferably from 10 to 80% by weight, basedon the weight of the binder resin.

<Binder resin>

As the binder resin in which the above respective components aredispersed, for example, there can be used various resins usedconventionally in the photosensitive layer.

There can be used, for example, thermoplastic resins such asstyrene-butadiene copolymer, styrene-acrylonitrile copolymer,styrene-maleic acid copolymer, acrylic copolymer, styrene-acrylic acidcopolymer, polyethylene, ethylene-vinyl acetate copolymer, chlorinatedpolyethylene, polyvinyl chloride, polypropylene, ionomer, vinylchloride-vinyl acetate copolymer, alkyd resin, polyamide, polyurethane,polycarbonate, polyacrylate, polysulfone, diallyl phthalate resin,ketone resin, polyvinyl butyral resin, and polyether resin;crosslinkable thermosetting resins such as silicone resin, epoxy resin,phenol resin, urea resin, and melamine resin; and photocurable resinssuch as epoxy acrylate and urethane acrylate. These binder resins can beused alone, or two or more kinds of them can be used in combination.

Particularly preferred resin includes, for example, bisphenol Z typemonomer and bisphenol Z type polycarbonate derived from phosgene, suchas Panlight manufactured by Teijin Chemicals Co., Ltd. and PCZmanufactured by Mitsubishi Gas Chemicals Co., Ltd.

The weight-average molecular weight of the binder resin is preferablywithin a range from 15,000 to 100,000.

In addition to the above respective components, various conventionallyknown additives such as antioxidants, radical scavengers, singletquenchers, deterioration inhibitors (e.g. ultraviolet absorbers),softeners, plasticizers, surface modifiers, extenders, thickeners,dispersion stabilizers, waxes, acceptors, and donors can be incorporatedinto the single-layer type electrophotosensitive material of the presentinvention as far as these additives do not exert a deleterious influenceon electrophotosensitive characteristics. To improve the sensitivity ofthe photosensitive layer, for example, known sensitizers such asterphenyl, halonaphthoquinones, and acenaphthylene may be used incombination with the electric charge generating material.

In the single-layer type electrophotosensitive material, a barrier layermay be formed between the conductive substrate and photosensitive layeras far as it does not inhibits the characteristics of the photosensitivematerial.

In the single-layer type electrophotosensitive material of the presentinvention, the film thickness of the photosensitive layer is preferablywithin a range from about 10 to 35 μm. When the film thickness exceeds35 μm, the memory becomes large. The reason is considered as follows.That is, as the film thickness of the photosensitive layer increases,dark decay increases to reduce the charging capability, whereby aninfluence of the memory is liable to be exerted. Alternatively, a trapincrease by an increase in absolute quantity of the constitutingmaterials of the photosensitive layer. On the other hand, when the filmthickness is less than 10 μm, the sensitivity is drastically lowered byremoval of the film, thereby making it difficult to put into practice.

As described hereinbefore, the single-layer type electrophotosensitivematerial according to the present invention includes a preferableembodiment which contains a compound represented by the general formula(1) as the hole transferring material and a compound represented by thegeneral formula (2) as the electron transferring material. Especially,it is more preferably to select HTM-1 as a compound represented by thegeneral formula (1) and ETM-1 as a compound represented by the generalformula (2).

The single-layer type electrophotosensitive material comprises aconductive substrate and a single photosensitive layer formed on theconductive substrate. This photosensitive layer is formed by dissolvingor dispersing the electric charge generating material, hole transferringmaterial, electron transferring material and binder resin in a propersolvent, coating the conductive substrate with the resulting coatingsolution and drying the coating solution.

As the conductive substrate on which the photosensitive layer is formed,for example, various materials having the conductivity can be used.Examples thereof include metallic simple substances such as iron,aluminum, cooper, tin, platinum, silver, vanadium, molybdenum, chromium,cadmium, titanium, nickel, palladium, indium, stainless steel, andbrass; plastic materials prepared by depositing or laminating the abovemetal; and glasses coated with aluminum iodide, tin oxide, and indiumoxide.

The conductive substrate may be in the form of a sheet or drum accordingto the structure of the image forming apparatus to be used. Thesubstrate itself may have the conductivity, or the surface of thesubstrate may have the conductivity. The conductive substrate may bepreferably those having a sufficient mechanical strength on use.

When the photosensitive layer is formed by the coating method, adispersion is prepared by dispersing and mixing the above holetransferring material, electric charge generating material, electronacceptor and binder resin, together with a proper solvent, using a knownmethod such as roll mill, ball mill, attritor, paint shaker, andultrasonic dispersing equipment, and then the resulting dispersion iscoated by using a known means and dried.

As the solvent for preparing the dispersion, various organic solventscan be used. The organic solvent includes, for example, alcohols such asmethanol, ethanol, isopropanol, and butanol; aliphatic hydrocarbons suchas n-hexane, octane, and cyclohexane; aromatic hydrocarbons such asbenzene, toluene, and xylene; halogenated hydrocarbons such asdichloromethane, dichloroethane, chloroform, carbon tetrachloride, andchlorobenzene; ethers such as dimethyl ether, diethyl ether,tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycoldimethyl ether; ketones such as acetone, methyl ethyl ketone, andcylohexanone; esters such as ethyl acetate and methyl acetate; anddimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide. Thesesolvents can be used alone, or two or more kinds of them can be used incombination.

To improve the dispersion properties of the hole transferring material,electric charge generating material and electron acceptor, and thesmoothness of the surface of the photosensitive layer, for example,surfactants and leveling agents may be used.

On the other hand, the image forming apparatus of the present inventionis a reversal development type digital image forming apparatus using thesingle-layer type electrophotosensitive material of the term (1),comprising at least a principal charge step, an exposure step, adevelopment step and a transfer step along the forward direction of theelectrophotosensitive material, characterized in that a voltage to beapplied in the transfer step has a polarity reverse to a voltage to beapplied in the charge step. Examples of the image forming apparatusinclude digital copying machine, facsimile and laser beam printer.

Even if the single-layer type electrophotosensitive material of thepresent invention is used in the above image forming apparatus includingno charge neutralizing step, no memory image is generated because ofvery small transfer and exposure memories.

As described above, the cleaning step may be omitted sometimes, similarto the charge neutralizing step, in order to reduce the size of theimage forming apparatus and initial cost.

EXAMPLES

The following Examples and Comparative Examples further illustrate thepresent invention in detail. The following embodiments are illustrative,and they should not be construed to limit the technical scope of thepresent invention.

Examples 1 to 8

2.0 Parts by weight of a X type metal-free phthalocyanine (CGM-1) as theelectric charge generating material, 70 parts by weight of a holetransferring material (HTM-1) represented by the general formula (1), 40parts by weight of electron transferring materials (ETM-1 to ETM-8)represented by the general formulas (2), (3), (4) and (5), 100 parts byweight a bis-Z type polycarbonate resin having a weight-averagemolecular weight of 30,000 as the binder resin and 800 parts by weightof tetrahydrofuran were dispersed or dissolved in a ball mill for 24hours to prepare a coating solution for single-layer type photosensitivelayer. Then, an alumina tube as the substrate was coated with thecoating solution according to a dip coating method, followed by hot-airdrying at 125° C. for 30 minutes to form a single-layer typephotosensitive material having a photosensitive layer of 20 μm in a filmthickness.

Comparative Examples 1 to 3

In the same manner as in Examples 1 to 7, except that ETM-9 to ETM-11were used as the electron transferring material, single-layer typephotosensitive materials were produced.

Examples 9 to 16

In the same manner as in Examples 1 to 8, except that titanylphthalocyanine (CGM-2) was used as the electric charge generatingmaterial, single-layer type photosensitive materials were produced.

Comparative Examples 4 to 6

In the same manner as in Comparative Examples 1 to 3, except thattitanyl phthalocyanine (CGM-2) was used as the electric chargegenerating material, single-layer type photosensitive materials wereproduced.

With respect to the single-layer type photosensitive materials of therespective Examples and Comparative Examples, the following respectivecharacteristics were evaluated. The evaluation results are shown inTables 1 and 2. Among these data, a relationship between a transfermemory potential, an exposure memory potential, and a difference inabsolution value between a plus polarity sensitivity and a minuspolarity sensitivity is shown in FIG. 1.

<Evaluation of plus polarity sensitivity>

Using a drum sensitivity tester (manufactured by GENTEC Co. under thetrade name of GENTEC SINCIA 30 M)), a voltage was applied to theelectrophotosensitive materials of the respective Examples andComparative Examples to charge the surface at +800 V. Then, the surfaceof each photosensitive material (exposure time: 100 msec 50 msec.) wasirradiated (exposure energy: 1.0 μJ/cm²) with monochromic light having awavelength of 780 nm (half-width: 20 nm, light intensity: 20 μW/cm²)from white light of a halogen lamp as an exposure light source through aband-pass filter, and then a surface potential at the time at which 500msec. have passed since the beginning of exposure was measured as apotential after exposure V_(LP) (V). The smaller the potential afterexposure, the higher the sensitivity of the photosensitive material.

[Evaluation of minus polarity sensitivity]

In the same manner as in case of the <evaluation of plus polaritysensitivity>, except that a voltage was applied to theelectrophotosensitive materials of the respective Examples andComparative Examples to charge the surface at −800 V using a drumsensitivity tester (manufactured by GENTEC Co. under the trade name ofGENTEC SINCIA 30 M)), a surface potential at the time at which 500 msec.have passed since the beginning of exposure was measured as a potentialafter exposure V_(LN) (V)

<Evaluation of transfer memory potential>

After the electrophotosensitive materials of the respective Examples andComparative Examples were installed in a multifunction printer Antico 40excluding a charge neutralizing lamp, manufactured by KYOCERA-MITA Co.,Ltd., a surface potential on application of no transfer bias and asurface potential on application of a transfer bias after the followingcharge step were measured and a difference between them was taken as atransfer memory potential. The case where the transfer memory potentialis 45 V or less at which no transfer memory image is generated was rated“Pass”, whereas, the case where the transfer memory potential is 45 V ormore was rated “Fail”.

<Evaluation of exposure memory potential>

After the electrophotosensitive materials of the respective Examples andComparative Examples were installed in a multifunction printer Antico 40excluding a charge neutralizing lamp, manufactured by KYOCERA-MITA Co.,Ltd., a surface potential on no exposure and a surface potential onexposure after the following charge step were measured and a differencebetween them was taken as an exposure memory potential. Similar to thecase of the transfer memory potential, the case where the exposurememory potential is 45 V or less at which no transfer memory image isgenerated was rated “Pass”, whereas, the case where the exposure memorypotential is 45 V or more was rated “Fail”.

<Evaluation of transfer memory image>

After the electrophotosensitive materials of the respective Examples andComparative Examples were installed in a multifunction printer Antico 40excluding a charge neutralizing lamp, manufactured by KYOCERA-MITA Co.,Ltd., a printing test was carried out and it was visually judged whethera transfer memory image is generated or not. As shown in FIG. 2, thetransfer memory image refers to an image wherein a black lateral bandwas generated in a drum longitudinal direction by a reduction in surfacepotential of the photosensitive material at the portion to which thetransfer bias was applied in case where the printing test was carriedout using an original having a gray front surface (Munsell value:N=6.5).

<Evaluation of exposure memory image>

After the electrophotosensitive materials of the respective Examples andComparative Examples were installed in a multifunction printer Antico 40excluding a charge neutralizing lamp, manufactured by KYOCERA-MITA Co.,Ltd., a printing test was carried out and it was visually judged whetheran exposure memory image is generated or not. The exposure memory imagerefers to an image wherein a ghost image of the exposed portion wasgenerated at the gray portion by a reduction in surface potential of thephotosensitive material at the strongly exposed portion (black solidportion) in case where the printing test was carried out using anoriginal as shown in FIG. 3.

TABLE 1 Plus Minus Difference in Transfer Exposure Exposure polaritypolarity absolute value memory memory memory Kind of sensitivitysensitivity of sensitivity potential potential Transfer potential ETM(V) (V) (V) (V) (V) memory image (V) Example 1 ET-1 132 150 18 15 10 Nomemory image No memory image was generated was generated Example 2 ET-2141 290 149 20 26 No memory image No memory image was generated wasgenerated Example 3 ET-3 144 341 197 30 32 No memory image No memoryimage was generated was generated Example 4 ET-4 150 352 202 26 10 Nomemory image No memory image was generated was generated Example 5 ET-5131 153 22 15 25 No memory image No memory image was generated wasgenerated Example 6 ET-6 205 322 117 35 32 No memory image No memoryimage was generated was generated Example 7 ET-7 252 550 298 35 36 Nomemory image No memory image was generated was generated Example 8 ET-8223 704 481 25 44 No memory image No memory image was generated wasgenerated Comp. ET-9 131 652 521 55 66 Lateral black Ghost image wasExample 1 band was generated generated Comp. ET-10 123 663 540 70 76Lateral black Ghost image was Example 2 band was generated generatedComp. ET-11 130 661 531 85 90 Lateral black Ghost image was Example 3band was generated generated

TABLE 2 Plus Minus Difference in Transfer Exposure Exposure polaritypolarity absolute value memory memory memory Kind of sensitivitysensitivity of sensitivity potential potential Transfer potential ETM(V) (V) (V) (V) (V) memory image (V) Example 9 ET-1 109 128 19 13 4 Nomemory image No memory image was generated was generated Example 10 ET-2112 250 138 18 24 No memory image No memory image was generated wasgenerated Example 11 ET-3 109 312 203 24 29 No memory image No memoryimage was generated was generated Example 12 ET-4 115 320 205 22 5 Nomemory image No memory image was generated was generated Example 13 ET-5108 322 14 13 25 No memory image No memory image 122 was generated wasgenerated Example 14 ET-6 173 290 117 32 30 No memory image No memoryimage was generated was generated Example 15 ET-7 211 523 312 33 30 Nomemory image No memory image was generated was generated Example 16 ET-8189 675 486 20 42 No memory image No memory image was generated wasgenerated Comp. ET-9 100 623 523 56 60 Lateral black Ghost image wasExample 4 band was generated generated Comp. ET-10 95 630 535 68 70Lateral black Ghost image was Example 5 band was generated generatedComp. ET-11 103 620 517 90 86 Lateral black Ghost image was Example 6band was generated generated

As is apparent from Table 1, Table 2 and FIG. 1, when a difference inabsolute value between a plus polarity sensitivity and a minus polaritysensitivity is 500 V or less, both of a transfer memory potential and anexposure memory potential becomes 45 V or less so that no memory imageis generated.

The disclosure of Japanese Patent Application Serial No. 11-302914,filed on Oct. 25, 1999, is incorporated herein by reference.

What is claimed is:
 1. A single-layer type electrophotosensitivematerial comprising a conductive substrate and a photosensitive layerformed on the conductive substrate, characterized in that thephotosensitive layer contains a phthalocyanine compound as an electriccharge generating material, a hole transferring material and an electrontransferring material in a binder resin, and that a difference inabsolute value between a plus polarity sensitivity and a minus polaritysensitivity measured under the conditions of an exposure wavelength of780 nm and an exposure energy of 1.0 μJ/cm² is not more than 500 V 312V, wherein the single-layer type electrophotosensitive material is usedin a method including charging the electrophotosensitive material,exposing an image to form a static latent image, developing the staticimage to form a toner image, and transferring the toner image along aforward direction of the electrophotosensitive material, the method notincluding a charge neutralizing step.
 2. The single-layer typeelectrophotosensitive material according to claim 1, wherein theabsolute value of the plus polarity sensitivity is smaller than that ofthe minus polarity sensitivity.
 3. The single-layer typeelectrophotosensitive material according to claim 2, which contains, asthe hole transferring material, a compound represented by the generalformula (1):

wherein R¹ and R³ are the same or different and each represents an alkylgroup which may have a substituent, an aryl group which may have asubstituent, or an aralkyl or alkoxy group which may have a substituent;and R² and R⁴ are the same or different and each represents a hydrogenatom, or an alkyl or alkoxy group which may have a substituent, providedthat R² and R⁴ are hydrogen atoms when R² and R⁴ are substituted at thepara-position.
 4. The single-layer type electrophotosensitive materialaccording to claim 2, which contains, as the electron transferringmaterial, at least one selected from the group of compounds representedby the general formula (2):

wherein R⁵ represents a halogen atom, or an alkyl or aryl group whichmay have a substituent; and R⁶ represents an alkyl or alkoxy group whichmay have a substituent, or a group: —O—R^(6a), which represents an alkylor aryl group which may have a substituent; the general formula (3):

wherein R⁷ and R⁸ are the same or different and each represents an alkylgroup, a halogenated alkyl group, an aryl group, an aralkyl group, analkoxy group, an aryloxy group, an aralkyloxy group, an acyl group, analkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonylgroup, or a nitro group; and n represents an integer of 0 to 3; thegeneral formula (4):

wherein R^(9a), R^(9b), R^(9c) and R^(9d) are the same or different andeach represents a hydrogen atom, or an alkyl or aryl group which mayhave a substituent; and the general formula (5):

wherein R¹⁰ and R¹¹ are the same or different and each represents analkyl group, a halogenated alkyl group, an aryl group, an aralkyl group,an alkoxy group, an aryloxy group, an aralkyloxy group, an acyl group,an alkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonylgroup, or nitro group; and n represents an integer of 0 to
 3. 5. Thesingle-layer type electrophotosensitive material according to claim 2,which contains, as the hole transferring material, a compoundrepresented by the general formula (1) and, as the electron transferringmaterial, a compound represented by the general formula (2).
 6. Thesingle-layer type electrophotosensitive material according to claim 2,wherein the content of the phthalocyanine compound is from 0.1 to 4.0%by weight based on the weight of the binder resin.
 7. The single-layertype electrophotosensitive material according to claim 2, whichcontains, as the binder resin, a bisphenol Z type polycarbonate resinhaving a weight-average molecular weight of 15,000 to 100,000.
 8. Thesingle-layer type electrophotosensitive material according to claim 2,wherein the film thickness of the photosensitive layer is from 10 to 35μm.
 9. A method of producing a single-layer type electrophotosensitivematerial comprising a conductive substrate and a photosensitive layerformed on the conductive substrate, the photosensitive layer containinga phthalocyanine compound as an electric charge generating material, ahole transferring material and an electron transferring material in abinder resin, characterized in that the photosensitive layer is formedby selecting the phthalocyanine compound, hole transferring material,electron transferring material and binder resin so that a difference inabsolute value between a plus polarity sensitivity and a minus polaritysensitivity is not more than 500 312 V under the measuring conditions ofan exposure wavelength of 780 nm and an exposure energy of 1.0 μJ/cm².10. The method of producing a single-layer type electrophotosensitivematerial according to claim 9, wherein said electron transferringmaterial is at least one member selected from the group consisting of acompound of formula (2):

wherein R⁵ represents a halogen atom, or an alkyl or aryl group whichmay have a substituent; and R⁶ represents an alkyl or alkoxy group whichmay have a substituent, or a group: —O—R^(6a), which represents an alkylor aryl group which may have a substituent; the formula (3):

wherein R⁷ and R⁸ are the same or different and each represents an alkylgroup, a halogenated alkyl group, an aryl group, an aralkyl group, analkoxy group, an aryloxy group, an aralkyloxy group, an acyl group, analkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonylgroup, or a nitro group; and n represents an integer of 0 to 3; theformula (4):

wherein R^(9a), R^(9b), R^(9c) and R^(9d) are the same or different andeach represents a hydrogen atom, or an alkyl or aryl group which mayhave a substituent; and the formula (5):

wherein R¹⁰ and R¹¹ are the same or different and each represents analkyl group, a halogenated alkyl group, an aryl group, an aralkyl group,an alkoxy group, an aryloxy group, an aralkyloxy group, an acyl group,an alkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonylgroup, or nitro group; and n represents an integer of 0 to
 3. 11. Amethod for reversal development in a digital image forming apparatuscomprising charging the apparatus with the single-layer typeelectrophotosensitive material of claim 1, carrying out an exposure ofexposing an image to form a static latent image, developing said staticlatent image to form a toner image, and transferring said toner imagealong a forward direction of the electrophotosensitive material, whereina voltage is applied in the transferring which has a polarity reverse toa voltage to be applied in the charging, further wherein the method doesnot include a charge neutralizing step.